In Blake's, "London," the speaker uses an adult narrator who is walking through the streets of London, a city that is not only the capitol of England, but the capitol of the British Empire. The city, as the speaker experiences it, falls short of what it should be, in the speaker's (and Blake's, by extension) perception.
Humans suffer under charters, regulations, popular opinions and mores, which all lead to "mind-forged manacles."
The speaker uses rhyme, with every other line rhyming in each stanza. He uses repetition: "In every..."; "charter'd"; "mark" and "Marks"; "cry." He uses alliteration: "And the hapless Soldiers sigh...."
The poem also uses allusion, referring to the "Chimney-sweepers" who appear in other poems in Blake's collections Songs of Innocence and Songs of Experience (in which "London" is included).
Rhyme, repetition, consistency of theme, and the linear walk through the streets of the narrator, create unity in the poem, with the speaker's opening of the final stanza leading to the final thoughts:
But most thro' midnight streets I hear....
And in the final stanza we see what sex and marriage in London lead to, what women having to sell themselves to survive leads to, and what marriage that must be maintained because society says so leads to.
EVery BLACKning CHURCH apPALLS,
RUNS in BLOOD down PALace WALLS
HOW the YOUTHful HARlots CURSE
There is a heavy emphasis in each of the three words, "youthful harlots curse," because Blake thinks this is the worst spectacle to be seen and heard in London. The harlots could be very youthful indeed. Many might still be children. It is because so many of them are so young that the image is so terrible. The entire poem seems to be marching towards that image in the last stanza. The youthful harlots are destined to get syphilis and other sexually transmitted diseases, and these can be passed on to many men, who can pass them on to their innocent wives when they get married, and the women's newborn infants can be born with a disease that will grow with them as they mature, since those diseases were incurable. That is why he says that the youthful harlots curse
And blights with plagues the Marriage hearse
And BLIGHTS with PLAGUES the MARRiage HEARSE
When the evening is spread out against the sky
Like a patient etherized upon a table;
Let us go through certain half-deserted streets,
The muttering retreats
Of restless nights in one-night cheap hotels
And sawdust restaurants with oyster shells:
Streets that follow like a tedious argument
Of insidious intent